1. Field of the Invention
The present invention relates to a reinforced structure for a cabin of a working machine such as a hydraulic excavator.
2. Description of the Related Art
In this type of a working machine, a relatively large opening is formed in a box-shaped cabin in order to ensure a visual field as wide as possible during a work. On the other hand, in the case of a large-sized working machine, its weight reaches several ten tons, and therefore it is necessary to ensure sufficient rigidity of the cabin to prevent damage even if such a large-sized working machine falls down.
Various reinforced structures have so far been proposed to strengthen the cabin rigidity while ensures the visual field.
For example, in Japanese Patent Laid-Open Publication No. 2004-345486, there is disclosed a reinforced structure wherein frame-like reinforcing members are arranged along pillars which constitute a framework of a cabin.
In Japanese Patent Laid-Open Publication No. 2007-69822, there is disclosed a reinforced structure wherein a first reinforcing member for reinforcing a front edge portion of a roof window and a second reinforcing member for reinforcing the portion from behind the roof window up to a rear window can be combined together selectively in accordance with the weight of a hydraulic excavator.
However, in the case of such a large-sized working machine as weighs several ten tons, a mere additional reinforcement of the cabin framework as in the reinforced structures disclosed in the above patent literatures leaves uneasiness in point of rigidity.
Further reinforcement can be effected by enlarging a reinforcing member, but the material cost and weight increase and the reinforcing member gets into the visual field, thus deteriorating the same field. The reinforcing member disposed along an upper front edge of the cabin is particularly gets into the visual field during a work so as to easily be an obstacle.
Increasing the number of members for reinforcement may be effective, but this is also disadvantageous in point of material cost and weight. Accordingly, it is preferable to constitute a simple reinforced structure which is reduced in the number of members used.